1. Field of the Invention
The invention relates to a device for exhaust gas after treatment of motor vehicles, in particular, diesel engine vehicles, comprising at least one pump device for supplying a solution to an exhaust gas manifold.
2. Description of the Related Art
For exhaust gas after treatment in diesel combustion engines, preferably in trucks and passenger cars, a significant reduction of nitrogen oxide emissions is demanded. In the past, by means of a commercially available pump the required amount of an aqueous urea solution was pumped from a storage tank and, at a certain pressure, supplied via a filter to an injection valve. The supply line may comprise additionally a hydraulic storage element. The injection valve meters the desired amount of aqueous urea solution into a stream of air. This stream of air is taken from the network provided on board the vehicle and is supplied via a shut-off valve at a certain pressure, adjusted by means of a pressure reducing valve, into a mixing path. This stream of air entrains the injected aqueous urea solution. This mixture or mist is supplied via a supply line to the injection valve provided at the exhaust gas manifold and is injected upstream of a selective catalytic reduction (SCR) catalytic converter into the exhaust gas flow. The quantity of aqueous urea solution added in this way must be supplied via the injection valve as a function of the current operating state of the vehicle in a extremely precisely metered quantity. However, with such injection valves, such extremely precise metering actions can be achieved only with difficulty. Moreover, this precise metering cannot be ensured over an extended period of time.